The tops of the keys of many keyboards, such as computer keyboards, bear identifying indicia--letters, numbers, symbols, or a combination thereof. In the past, keyboard indicia have been created by ways that vary from expensive two-shot molding techniques (which create deeply embedded, long wearing indicia) to relatively inexpensive surface printing techniques (which create a surface image that wears away with time and use). Recently, keyboard manufacturers have begun to use wet and dry diffusion printing techniques to create indicia in the tops of the keys. Both techniques have the advantage that they are less expensive that two-shot molding and create infused indicia images whose wear life is considerably greater than surface printed images.
In wet diffusion printing, a dye is transferred from an ink plate to the part using conventional stamping pad equipment. Colors are applied one at a time and the surface of the part that is to receive the dye must be precleaned to insure that no contaminants interfere with the printing process. In addition, the keys must be post-cured to set the images. These disadvantages are avoided by dry diffusion printing.
In dry diffusion printing, a transfer paper onto which the image has been preset is pressed against the key that is to receive the indicia. The pressure plus heat results in the dye that forms the indicia image being transferred from the transfer sheet to the key. Image transfer to several keys (including an entire keyboard) can take place simultaneously. Dry diffusion printing requires no prior part cleaning since dye transfer can take place through most surface contaminants. Further, no post-curing is required. In dry diffusion printing, dry dye crystals sublimate upon heated contact with the resin that forms the keys. That is, the dry dye crystals change directly from a solid form into a gas and back into a solid without going through a liquid phase. Attractive forces between the dry dye crystals and the resin molecules "pull" the image into the part. The end result of this migration is a sharp, abrasion-proof image infused to a depth of 4-6 ml. Since dry dye crystals are transferred from a pattern preset on the transfer paper, multi-colored images can be transferred in a single step.
In the past, dry diffusion printing machines designed to apply heat and pressure to a sheet of transfer paper to cause the dye crystals that form images to be transferred from the paper to the tops of the keys have been developed. Most such machines currently in use do not print assembled keyboards. Rather only individual keys are printed. Hence, these machines require the labor intensive operation of loading loose keys into a printing fixture prior to printing. After printing, the keys must be removed from the fixture and accurately mounted in a keyboard frame or housing. The repetitive nature of this task makes the probability of error high. The present invention is directed to avoiding these and other problems, and providing a new and improved dry diffusion printing machine that simultaneously prints indicia on the keys of an assembled keyboard.